We show direct evidence for importance of the interface resistance to electrically create large spin accumulation in silicon (Si). With increasing the thickness of the tunnel barrier in CoFe/MgO/n+-Si devices, a marked enhancement of spin accumulation signals can be observed in the electrical Hanle-effect measurements. To demonstrate room-temperature detection of the spin signals in three-terminal methods, the influence of the spin absorption from Si into CoFe through a tunnel barrier should be taken into account.
We experimentally demonstrate a giant voltage-controlled magnetic anisotropy (VCMA) coefficient in a crystallographically strained CoFe layer (>15 monolayers in thickness) in a MgO/CoFe/Ir system. We observed a strong applied voltage dependence of saturation field and an asymmetric concave behavior with giant VCMA coefficients of %758 and 1043 fJ V %1 m %1 . The result of structural analysis reveals epitaxial growth in MgO/ CoFe/Ir layers and the orientation relationship MgO(001) [110] k CoFe(001)[100] k Ir(001) [110]. The CoFe layer has a bcc structure and a tetragonal distortion due to the lattice mismatch; therefore, the CoFe layer has a large perpendicular magnetic anisotropy.
We investigate spin transport and accumulation in n+-Si using Heusler compound Co2FeSi/MgO/Si on insulator (SOI) devices. The magnitudes of the non-local four- and three-terminal Hanle effect signals when using Heusler compound Co2FeSi/MgO/SOI devices are larger than when using CoFe/MgO/SOI devices, whereas the preparation methods of MgO layers on SOI are exactly same in both devices. Different bias voltage dependencies on the magnitude of spin accumulation signals are also observed between these devices. Especially, Co2FeSi/MgO/SOI devices show large spin accumulation signals compared with CoFe/MgO/SOI devices in the low bias voltage region less than ∼1000 mV in which the increase of the spin polarization is expected from the estimation of the density of states in Heusler compound Co2FeSi and CoFe under spin extraction conditions. These results indicate that the species of ferromagnetic material definitely affects the magnitude and behavior of the spin signals. The use of highly polarized ferromagnets such as Heusler compounds would be important for improving the spin polarization and the magnitude of spin signals through Si channels.
Local magnetoresistance (MR) through silicon (Si) and its bias voltage (Vbias) (bias current (Ibias)) dependence in ferromagnet (FM)/MgO/silicon-on-insulator lateral spin valves are investigated. From the experimental measurements, we find that the local-MR through Si increases with increasing Vbias. This anomalous increase of local-MR as a function of Vbias can be understood by considering the standard drift-diffusion theory improved by taking into account the difference in the interface resistances and first order quantum effect between FM/MgO/Si (source) and Si/MgO/FM (drain) interfaces. The interface resistance dependence on experimentally obtained local-MR ratios also agrees with the improved standard spin diffusion theory. These results indicate that experimentally observed local-MR is certainly related to the spin signal through the Si bulk band.
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